The present disclosure relates generally to systems, methods, and devices for facilitating access to a target anatomical site. More specifically, methods and structures are provided for detecting and facilitating positioning of a probe in a vascular tissue of a patient, such as a patient's vein for central line or catheter placement.
Needles and catheters are routinely inserted or injected into a patient's body for various purposes or indications. One type of indication that involves such insertion is the placement of vascular lines or catheters, for instance, the placement of a central venous catheter (CVC). A CVC is typically used to administer fluids (e.g., intravenous (IV) drugs, chemotherapeutic agents, blood, or saline) into the body in medical situations in which large fluid transfer volume and/or high fluid transfer rate is desired. Common CVC insertion targets include an internal jugular vein, located in the neck; a subclavian vein, located in the chest; or a femoral vein, located in the groin.
During a central line procedure, a large tube (cannula) called a catheter is inserted into a central vein, like the internal jugular vein in the neck or the subclavian vein under the collarbone. Large arteries, like the carotid artery, lie next to these veins, and putting the catheter into the artery by accident (arterial cannulation) can result in serious injury, stroke or even death. In the event that a large bore catheter is accidentally inserted into an artery, emergency surgery is usually required to remove the catheter and repair the artery. To avoid arterial cannulation, the Seldinger technique was developed where a small introducer needle is used to locate the vein, before inserting the much larger catheter. The small needle can be safely removed from an artery or a vein—it only makes a small hole that is able to seal after the needle is removed. In this technique, a small introducer needle is attached to a syringe and the needle is inserted into the vessel. Blood is pulled back (aspirated) through the needle and into the syringe, and the color of the blood in the syringe is used to determine whether the introducer needle is an artery or a vein. Arterial blood is usually bright red and venous blood is darker. However, in sick patients this is not always true—arterial blood could appear quite dark in a patient with low blood oxygen levels.
Once the physician confirms that the needle is in the vein using the color of the blood, the syringe is removed and the blood is allowed to flow directly out the rear of the needle. If the blood “spurts” out the back of the needle, it is an indication that the needle might be in an artery. If the blood comes out of the needle slowly, the needle is likely in a vein. Unfortunately, there are many reasons why arterial blood might not “spurt” out of the needle, and so this method for identifying an artery is also prone to error. After looking at the blood color and pulsatility, if the physician decides that the needle is in a vein, a small flexible guidewire is inserted through the needle. The introducer needle is then removed and the catheter is inserted over the guidewire. The guidewire ensures that the catheter enters the vein.
A problem with CVC placement via the Seldinger technique alone is that misplacement of either or both of the needle and the CVC is still far too common. For example, an unintended puncture or tear of a venous wall and/or the placement of one or both of the needle and the CVC into an artery (i.e., an unintended arterial cannulation) can occur, which may result in serious and expensive complications including severe bleeding, emergency vascular surgery, stroke, and possibly death. Moreover, the Seldinger technique, which relies on both blood color and pulsatility to differentiate a vein from and artery, does not always prevent accidental arterial cannulation, and this error happens in as many as 1 out of every 100 procedures.
Manometry is a technique that has been used for verifying that an appropriate type of blood vessel has been targeted during catheterization (e.g., in association with the Seldinger technique). See, e.g., FIGS. 2A-F. Conventional manometry directed toward vascular target verification includes an extension set (e.g., a 50 centimeter extension tube set) attached to a needle or a catheter (e.g., an 18-gauge needle or catheter) that has been inserted into a vessel. Blood flows or is drawn from the patient's body into the needle or catheter, and further flows into an elevated section of tube along the extension set, thereby forming a blood column indicative of probe positioning (e.g., column height, color, pulsatility). The height attained by the blood column, e.g., gives an indication as to the pressure of the blood within the vessel under consideration. Such an assessment can enable the practitioner to verify a venous or an arterial placement of the needle or the catheter. However, needle or catheter occlusion or patient state or condition can impact the visible properties of the blood column, and hence the surgeon's assessment, which can lead to a false conclusion about needle or catheter placement. For instance, in a hypotensive patient, an inadvertent arterial needle insertion may not be readily apparent from a naked-eye assessment of blood column height within the elevated section of tube.
Once the physician decides that the needle is in a vein using this blood column, he detaches the tubing from the needle and then proceeds to insert the guidewire through the needle, leaving a “blind spot” where monitoring for needle positioning does not occur. A risk with this technique is that the needle can move while attaching or detaching the tubing; it is possible the needle could move from a vein to an artery after the tubing has been removed. If this were to happen, the tube based pressure measurement would not prevent arterial cannulation. Further, widespread adoption of manometry has been severely limited by procedure awkwardness, additional time, equipment and steps required, and the increased chance of infection. Studies show that many physicians do not routinely utilize manometry for verifying needle or catheter placement for at least some of these reasons. Accordingly, manometry procedures are generally cumbersome and not routinely used, and even when used the risk of complication (e.g., accidental arterial puncture or cannulation, infection, etc.) has not been eliminated.
Ultrasound has been conventionally utilized for determining the position of objects within the body, and can be utilized for facilitating placement or positioning of needles, guidewires, and catheters. See, e.g., FIGS. 3A-D. Reduced expense and increased portability of ultrasound equipment has led to application of ultrasound imaging to guide central line placement. However, one aspect of ultrasound guidance particularly relevant to discussion of arterial cannulation, is that the needle and/or wire may not always be visualized in the target vein. Because of the tomographic nature of an ultrasound beam, it is sometimes difficult to distinguish a needle shaft from the needle tip. Thus, confusion between the tip and the shaft of the needle in an image can lead to inadvertent arterial cannulation when the needle passes through the target vein and into a nearby artery. Further, recent surveys show that widespread use of ultrasound equipment in vascular catheterization procedures is limited to a small minority of practitioners (e.g., as little as 15%). The relative expense, lack of accessibility, equipment sharing between multiple groups or departments, and need for additional medical personal may explain the limited use of ultrasound in central line placement. Additionally, ultrasound guidance is not particularly well suited to guide catheters inserted into the subclavian vein (the most common access vein used in trauma situations). The subclavian vein is beneath the collarbone, and the collarbone blocks the ultrasound signal. Further, ultrasound ties up one hand, forcing the physician to perform the procedure with a single hand. For this reason, a second person is often used to assist during ultrasound guided procedures.
Accordingly, improved methods and structures are needed for facilitating probe access and/or positioning in a target vascular tissue, and could significantly improve efficiency and reduce complications associated with many medical procedures, such as central line or catheter placement in a vein of a patient.